Chapter 9
Mg 2H01 My 42 H2
19
ESIN
Gases collection
Tests for anions &
Jar not measuring
cations
gas
Cylinder
delivery upward
lighterthan air
Deliverytube H2 1 1
20 288
Bung stopper
Downward delivery
Denser than Air
CO2 12 16 16 44728
Mr ofAir 28.8
86
This chapter is for paper 6 & must be learnt by heart
A. Collection of gases By Upward And Downward
Delivery
• Gases lighter than air are collected by upward delivery.
• Gases denser than air are collected by down ward delivery.
Upward Delivery Downward Delivery
Gas
a Jar
Delivery
e tube
To collect light gases To collect dense gases
Lighter than air Denser than air
(Mr < 28.8) (Mr > 28.8)
B. Measuring Volume Of Gases
The gas syringe is the Zero
ideal tool used to measure i is 20 2s the
plunger
volume of a gas at room
temperature and
atmospheric pressure (at
r.t.p.).
PIL byruler
in it in i i i i i
87
water solublegases
Acidicgases Alkalinegas For Mix s fgases
Insoluble
Nits to
f
Act502,50
Ammoniagas
A euta ch
C. Collection Of Gases Over Water:
NO2 g COz
The insoluble neutral gases can be collected over water because they do
not dissolve in water.
Examples are oxygen, nitrogen, hydrogen,
memorize
methane…etc.
Note:
1) Do not try to collect acidic gases or
04 alkaline gases over water because they
ie
GHQ are completely soluble in water. e.g : NH3,
2 water
HCl, SO2 , SO3 RemoveswaterFrommixtures
p 2915
2) The most abundant drying agent is
w
yy concentrated sulfuric acid.
3) This process could be also used for
trough
separating a mixture of different gases; e.g. when a mixture
of CO2 (acidic) & CH4 (neutral) is passed through an alkali
(NaOH), carbon dioxide dissolves & only methane is collected
over the liquid.
88
E. Tests for aqueous cations
Cation Effect of aqueous sodium Effect of aqueous ammonia
hydroxide (ammonia solution)
Ammonium Ammonia produced on warming
(NH4+)
Copper Light blue ppt., insoluble in Light blue ppt., soluble in excess.
(Cu2+) excess Giving a dark blue soluble
Iron II (Fe2+) Green ppt., insoluble in excess Green ppt., insoluble in excess
Iron III Red – brown ppt., insoluble in Red – brown ppt., insoluble in
(Fe3+) excess excess
Chromium III Green ppt., soluble in excess Grey-green ppt., insoluble in
(Cr3+) excess
Zinc (Zn2+) White ppt., soluble in excess, White ppt., soluble in excess,
giving a colourless solution giving a colourless solution
Aluminium White ppt. soluble in excess White ppt., insoluble in excess
(Al3+) giving a colourless solution
Calcium White ppt., insoluble in excess No ppt. or very slight white ppt.
(Ca2+)
NH3 gas
Al foil
NaOH
NH4+ NO3
N.B.: ammonia gas is liberated upon the reaction of ammonium salts
with any base (CaO) or alkali (NaOH)
F. Tests for gases
Gas Test and test result
Ammonia (NH3) Turns damp red litmus paper blue
Carbon dioxide Turns limewater milky
(CO2)
Chlorine (Cl2) Bleaches damp litmus paper
Hydrogen (H2) ‘pops’ with a lighted splint.
Oxyge (O2) Relights a glowing splint
Sulfur dioxide (SO2) Turns acidified aqueous potassium manganate (VII)
from purple to colourless
89
G. Flame tests for metal ions
Metal ion Flame colour
lithium (Li )
+
red
sodium (Na+) yellow
potassium (K+) lilac
Calcium ( Ca2+) Orange - red
Barium ( Ba2+) Light green
copper(II) (Cu2+) blue-green
How to perform a flame test:
1. Dip a Ni-Chrome wire /platinum wire in an aqueous solution
containing the cation then introduce it to the roaring flame of
Bunsen burner
2. Dip a Ni-Chrome wire/platinum wire in water then in the solid
salt then introduce it to the roaring flame of Bunsen burner
H. Further tests to be memorized
• Tests of water: Water turns anhydrous copper sulfate from white to blue
Water turns anhydrous cobalt chloride from blue to pink
• Test of ethanol: Ethanol is a neutral flammable liquid which burns &
catches fire with a blue or yellow flame & has an aromatic (antiseptic)
odour.
• Test of unsaturation: Unsaturated hydrocarbons (alkenes) decolorize
bromine water, while with saturated hydrocarbons (alkanes) color
(reddish brown) remains.
N.B.
• Tests performed by a Bunsen burner (continuous flame). Tests of aqueous
cations
• Tests performed by a lighted splint (match). Flammable substances (hydrogen,
oxygen, ethanol & organic compounds)
90
Tets For gases
Name Conclusion
Test Result Observations
Carbondioxide
CO Add limewater Colourless
Turns milky
Ammonia NHz Add damp red litmus paper Turns blue
Chlorine Cla Add damp litmus Paper Bleach or removes colour
Hydrogen H2 Lighted splint POPS POP Sound
oxygen 02 glowing splint Relight
Add Acidified AqueousPotassium
syffuy.de
SO purple Colourless
Manganate V
Reducing agent
Oxidizing agent Chill Decolorized
Flame tests salt Mtandum
Nameofcai.in's Flamecolour
How to carry aflametest
Lit Red
Diptheplatinum wire
Nat Yellow
or Nigghrome
N
in abeaker Contains the salt
kt Lilac
ions in aqueousform then introduce
Ca OrangeRed
to the bunsenburner and Observe
Bit Lightgreen
the Flame colour change
Ca Bluegreen
Hions
Tests For Cations 4 3 1
Nacaf Test Asd.fm
Test2iAddAqueou AmmoniaNHuO Ca2t
BYE Culott Blue
P Gissoneines
givingdark
Cr 979CroHl You
Felt 9 7 Felot Feldt k
Fe Felons B.fi Fel0HlsX
Disseless
FEE Insoluble
in excess
Ej oH
iitate
whitesolid
2 Al a
Dissolve
turns
White ppt Precipitate NaOH
NaOH NaOH Naoh NAOH NAOH
x x x
Cation Tests Foranions 6 1
Anion
NH Effate Name Conclusion
Test Result Observation
Animonium
cg Carpgate Add an acid 02 s
Decolonized
so sulfite add acidified Aqueous 502 kMnOy
warm Potassiummanganate
VI Purple to Colourless
50 Este Bason
while's
B
awaits fins 3 ions havesametest
CT chloride
Agel whiteppt
Adddampred
turnsblad Add ANG
Br Bromide AgBr Creamy Ppt
Then AgNg
ion
I Iodide ASI Yellow ppt
24
Ba 50 Baso
G
Agt CI Agc
Agt Br AgBr
Agt I AgI
91
